I got my hands on an older model Thudbuster LT about a month ago. I've quite enjoyed it so far and have spent a while fiddling with it & working out what suits me best. After the recent snow and ice the London roads are more mangled than ever, potholes abound, so the combination of fat tyres plus Thudbuster keeps me feeling reasonable safe. There's been a bit of a discussion over on the Dahon forums recently and I thought I'd repeat something I brought up there and add a few thoughts.
I read a review once, one of the only somewhat negative reviews that I've seen, stating that the arc of travel is contrary to what would be most efficient, i.e. what you really want to dissipate impact is first vertical motion which arcs into the horizontal. That makes sense but doesn't take into account the changing angle of the frame as the wheels respond to bumps, which is kind of the selling point of the Thudbuster. What I've found in riding it is that with quite stiff elastomers (the ones recommended for my weight) the beginning of the travel, er, vector, is very much horizontal, whereas with softer elastomers my weight compresses the elastomers more, so the early stage of travel is more vertical (further into the arc), and that's when it feels like the Thudbuster is working fairly well. One problem with that is that it also means the saddle position is further back, something I'm not keen on.
The preload adjustment is a misnomer as it's really a topping-out limiter. It doesn't change how the elastomers respond to your weight at all, it just sets the limit to the uppermost point of travel, and I guess can prevent a 'flappy' topping out with soft elastomers. The way to get real preload adjustment would be to insert spacers between the 2 elastomers. . . I suppose one could cut the black elastomers into thin discs and add them into the mix.
I used a TB LT for about a year; I preferred stiffer elastomers than the recommended and I liked it a lot. These days I have a Birdy, a Mini and a Moulton, all with rear suspension, making the TB redundant.